Usually, a tire cord is arranged inside the tire, a rubber near the tire cord locates far from the heat source during a tire vulcanization process and it is not easy to be vulcanized. Thus, N,N-dicyclohexyl-2-benzothiazol sulfenamide (DCBS) is used for vulcanization acceleration (JP-A-2005-239874).
It has been known that other sulfenamide accelerators, other thiazol accelerators and the like are used instead of DCBS. In case of using these vulcanization accelerators, since initial adhesion with a steel cord is not sufficient and the effect of recovering adhesion with a steel cord at hygrothermal aging is small, attempts to improve these effects have been carried out by compounding resorcinol, a hybrid cross-linking agent or a great deal of cobalt (JP-A-2006-328194).
However, excellent adhesion under high temperature vulcanization condition at preparing automotive tires cannot be attained by these attempts, there is a problem that the adhesion is not sufficient compared with DCBS. If a great deal of cobalt is used, strength at break of a rubber is lowered due to thermal oxidative degradation. And if resorcinol is used, strength at break of a rubber is lowered.